In the field of electronic components, for example, solid materials are bonded together during wafer bonding wherein silicon substrates, substrates having an oxide layer or nitride layer formed on a silicon or other substrate, or substrates of glass material are bonded together, during bonding of metal materials between electronic components in flip-chip processes, and during package sealing when preparing MEMS (Micro Electro Mechanical Systems).
When bonding substrates, it is common to raise the strength of the bonding interface by heating to a high temperature after contact to promote chemical reactions between the bonding substrates and atomic diffusion in the vicinity of the bonding interface (bonding with heat treatment).
For example, in a method for bonding silicon wafers, the surfaces of silicon wafers may be hydrophilized, the pair of wafers joined by a van der Waals force, then subjected to a heat treatment at about 1000° C. to obtain a firm bond. Additionally, in anodic bonding, silicon and heat-resistant glass can be firmly bonded by applying a high voltage of 1 kV at 400° C.
However, bonding methods involving heat treatments are limited by the types of substrates to which they can be applied. In particular, when bonding together substrates of different materials, the differences in the coefficients of thermal expansion between the materials may result in increased residual thermal stresses and cause mechanical damage to the bonded materials as the temperature falls to room temperature (standard temperature), and as the residual stress becomes higher, the bonded materials may be destroyed. Additionally, bonding methods involving heat treatments are difficult to apply to bonding of components having elements with low heat resistance and voltage resistance, such as MEMS.
Standard-temperature bonding methods have been proposed for performing substrate bonding at room temperature, in order to overcome the detrimental influence that bonding methods involving heat treatments have on substrate materials. In this type of room temperature bonding method, the substrate surface is treated to a surface treatment such as cleaning or activation by irradiating the substrate with a particle beam, and the surface-treated substrate surfaces are brought into contact in a vacuum at room temperature for bonding.
Such room temperature bonding methods extend the types of substrate materials that can be applied compared to bonding methods involving heat treatments, and have met with a degree of success. However, such room temperature bonding methods have constraints on their bonding environment conditions, such as needing to keep the atmosphere at a high vacuum after surface activation and transition to the bonding process within an extremely short period of time in order to minimize reoxidation of the substrate surface which has been surface-activated. Additionally, since the bonding mechanism must be provided as a portion of the processing vacuum system, the bonding mechanism tends to be complicated and expensive.